Rotary actuator

ABSTRACT

A rotary actuator comprising a rotor including a permanent magnet and a stator of magnetic material substantially surrounding the rotor. A force field is set up in the magnetic material of the stator, and the permanent magnet of the rotor adds to this field to apply magnetic forces to the rotor tending to rotate the latter. The rotary actuator has various features which contribute to a relatively long stroke and high torque output.

United States Patent Ray [ ROTARY ACTUATOR [72] Inventor: Ralph D. Ray, 834 Production Place, Newport Beach, Calif. 92660 [22] Filed: Nov. 20, 1970 21 Appl. No.: 91,359

[52] U.S. Cl. ..335/230, 335/272 [51] Int. Cl. ..ll0lf 7/08 [58] Field of Search ..335/229, 230, 276, 272, 268

[56] References Cited UNITED STATES PATENTS 3,177,385 4/1965 Montagu ..335/229 X 3,593,238 7/1971 Mori ..33S/272 X [451 Sept. 26, 1972 FOREIGN PATENTS OR APPLICATIONS 62,155 4/1944 Norway ..335/230 Primary Examiner-George l-larris Attorney-Smyth, Roston & Pavitt 571 I ABSTRACT A rotary actuator comprising a rotor including a permanent magnet and a stator of magnetic material substantially surrounding the rotor. A force field isset up in the magnetic material of the stator, and the permanent magnet of the rotor adds to this field to apply magnetic forces to the rotor tending to rotate the latter. The rotary actuator has various features which contribute to a relatively long stroke and high torque output.

7 Claims, 13 Drawing Figures PATENTEDsEm 1912 SHEET 2 [IF 3 M/UEMTO/Z:

W'M, MfM

Arron/n5 ROTARY ACTUATOR BACKGROUND OF THE INVENTION There have been many attempts to provide a rotary actuator having high torque and a relatively long, for example, 40, stroke. Consequently, the prior art is replete with devices whose purpose is allegedly to increase the torque or length of stroke. l-Ieretofore none of the devices has been satisfactory.

One such prior art device is a linear solenoid with a cam to change the linear motion of the solenoid into rotary motion. This unit is relatively expensive, complex, and large due to the need for the cam and the as sociated parts. Moreover, the stroke and torque are not as large as desired for many applications.

Another prior art device is the rotary solenoid, and this device is capable of producing only very low torque and has a very short stroke. The mag wheel is another prior art device. The mag wheel is an electromagnetically powered indicator having a rotor which is adapted to be accurately positioned at any of several different locations. The mag wheel is not an actuator or a driver and its torque is extremely low.

SUMMARY OF THE INVENTION The present invention provides an electromagnetically powered rotary actuator which has a long stroke and produces very high torque in relation to its power consumption and size, In addition the torque curve can be tailored to suit particular operating requirements. As used herein and unless otherwise indicated, the torque produced by the actuator has reference to the torque as measured at the output of the actuator.

Generally the rotary actuator includes a rotor and stator of magnetic material with the stator having one or more windings for providing a force field to drive the rotor. The torque produced by a device of this type is proportional to the flux and to the change of permeance. To increase the flux and hence the torque, the rotor includes a permanent magnet.

To further increase torque, the rotor is driven by forces of attraction and repulsion. Preferably each pole of the permanent magnet is acted upon by the electromagnetic force field to drive the rotor from an initial position to a second position.

For maximum torque, the stator includes first and second stator sections separated by first and second regions of relatively high reluctance with each of the stator sections extending for approximately 180. However, good results can be obtained if the stator extends for only approximately the arc of stroke of the rotor.

The regions of relatively high reluctance are small circumferentially of the axis of rotation, and accordingly, the stator sections are close together. With the actuator energized, lines of flux extend from the first stator section through only a peripheral region of the rotor and into the second stator section. Thus, the primary flux path from the stator to the rotor does not pass through significant portions of the permanent magnet which is of high reluctance.

Another feature of the invention is to construct a peripheral segment of the rotor of unmagnetized, highly permeable material. This can be accomplished by adding elements or shoes of highly permeable material to the permanent magnet. The increase in permeance created by the shoes contributes to torque.

Torque can be increased by providing a relatively high change of permeance. This is accomplished by appropriately shaping and orienting the rotor. For example, the rotor can be provided with first and second peripheral surface portions of different configurations intersecting at a zone of intersection. The rotor is oriented so that the zone of intersection will rotate past the region of relatively high reluctance. This causes a change of permeance due to the difference in distances between the stator sections and the first and second peripheral surface portions.

The rotor of the rotary actuator moves from an initial to a second position in response to energizing the windings. When the coils are de-energized, the rotor tends to return toward the initial position. The rotor seeks a position in the de-energized condition in which the axis of magnetization points at the region of relatively high reluctance. To augment the natural tendency of the rotary actuator to return toward the initial position, biasing means such as a spring may be employed as the actuator has more than adequate torque to overcome the return spring force.

Energization of the windings causes some electromagnetic force to be applied to the rotor tending to rotate the same. Thus, it is possible to plot a curve of angular position or displacement of the rotor versus torque applied to the rotor, and it is also possible to plot a curve of rotor displacement versus output torque of the actuator. With the present invention, it is possible to select the portion of the torque curve which will define the operating range of the particular actuator by controlling the initial and second positions of the rotor.

According to one practice of the present invention, the return spring is sized to pull the rotor back somewhat from the inherent position which it seeks when the windings are de-energized. By so doing, the starting point of the operating range of the torque curve is selected. To minimize the strength of the return spring required, the permanent magnet should have an axis of magnetization which is properly oriented relative to the permanent magnet. An advantage of using a relatively weak return spring is that useful or output torque is increased. If the rotor is pulled back too far, a heavy return spring is required, and if the rotor is not pulled back at all from its natural de-energized position, it may not be possible to obtain a long stroke such as 40.

The present invention provides several ways for tailoring the torque curve to suit particular requirements. One way to tailor the torque curve is to change the direction of the axis of magnetization relative to the permanent magnet. For example, by moving the axis of magnetization toward the zone of intersection referred to hereinabove, torque near the end of the stroke is increased.

Shaping of the torque curve can also be accomplished by shaping of the region of relatively high reluctance. .For example, if the region of relatively high reluctance extends somewhat circumferentially of the axis of rotation of the rotor the torque curve tends to flatten out.

If the highly permeable shoes are utilized, the torque curve can be tailored by shaping of the shoes. For example, by progressively narrowing the shoes in the direction of rotation of the rotor, the torque curve tends to flatten out. This change is the result of the change in permanence caused by shaping of the shoes.

The invention can best be understood by reference to the following description taken in connection with the accompanying illustrative drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of a rotary actuator constructed in accordance with the teachings of this invention.

FIG. 2 is a side elevational view taken generally along line 2-2 of FIG. 1.

FIG. 3 is an enlarged sectional view taken generally along line 3-3 of FIG. 1.

FIG. 4 is an enlarged view partially in section taken generally along line 4-4 of FIG. 3 with the rotary actuator in the de-energized condition.

FIG. 4a is a sectional view taken generally along line 4a-4a of FIG. 4.

, FIG. 4b is a sectional view similar to FIG. 4a showing a modification of the high reluctance region between stator sections.

FIG. 4c is a fragmentary elevational view of the modification shown in FIG. 4b taken generally along line 4c-4c of FIG. 4b.

FIG. 5 is a sectional view similar to FIG. 4 with the rotary actuator being in the energized condition.

FIG. 6 is. a sectional view similar to FIG. 4 of a second embodiment of the present invention with the rotary actuator being de-energized.

FIG. 7 is an elevational view of one of the shoes taken along line 7--7 of FIG. 6.

FIG. 8 is a sectional view similar to FIG. 6 with the rotary actuator being energized.

FIG. 9 is a view similar to FIG. 4 showing another embodiment of the invention in which the torque arm is movable in either direction from a center position.

- FIG. 10 is a fragmentary sectional view similar to FIG. 3 showing the return spring and the adjacent structurefor the embodiment of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show a rotary actuator 11 constructed in accordance with the teachings of this invention. The rotary actuator 11 has a pair of mounting apertures 13 to facilitate mounting of the actuator 11 on supporting structure (not shown). The rotary actuator 11 has a torque arm 15 which is pivotable between an initial or first position shown in FIGS. 1 and 2 in which the rotaryactuator 11 is de-energized and a second or final position shown in dashed lines in FIG. 1 in which the rotary actuator is energized. The torque arm 15 has a slot 17 in the outer end thereof adapted to receive a driven member 19 of some driven device (not shown) which the rotary actuator 1 1 is to actuate. The external device can be actuated by energizing the rotary actuator 11 to thereby move the driven member 19 from the full line position shown in FIG. 1 to the dashed line position shown in FIG. 1.

With reference to FIGS. 2-4a, the rotary actuator 11 includes first and second frame sections or stator sections. The stator sections 21 and 23 have arcuate cutout regions cooperating to define a cylindrical rotor. receiving aperture 29. As shown in FIG. 4a, the brass slug 25 extends axially of the rotor receiving aperture 29. The slug 27 also extends axially of the aperture 29.

The stator section 21 has an arcuate, upwardly opening slot 31 which receives the torque arm 15 and permits angular movement thereof relative to the stator section 21. Flanges 33 and 35 are formed integrally with the stator sections 21 and 23, respectively, as

shown in FIGS. 4 and 4a with the flanges 33 being I generally coplanar and with the flanges 35 being coplanar. The flanges 33 are parallel to the flanges 35.

Cores 37 and 39 of ferromagnetic material are mounted on the flanges 33 and 35 in generally parallel relationship. The cores 37 and 39 extend in a direction transverse to the axis of the rotor receiving aperture 29. Although the cores 37 and 39 may be connected to the flanges 33 and 35 in any desired manner, in the embodiment illustrated, each of the cores has a flared portion 41 flared radially outwardly to cooperate with a corresponding countersink in the adjacent flange. Each of the cores 37 and 39 has a tapped hole 42 at the lower end thereof to facilitate mounting of the rotary actuator. Coils 43 and 45 are wound on tubular bobbins 44 received on the cores 37 and 39, respectively. The coils 43 and 45 are preferably connected in series and are energizable through leads 46.

A rotor 47 is mounted on a shaft 49 for rotation within the rotor receiving aperture 29. The shaft 49 is in turn supported by a bearing 51 mounted on the stator sections 21 and 23. The bearing 51 is constructed of nonmagnetic material such as aluminum. Specifically, the bearing 51 includes a plate section 53 staked in a counterbore 55 formed in both of the stator sections 21 and 23. The bearing 51 has a tubular section 57 integral with the plate section 53. The tubular section 57 has a passage 59 which receives the shaft 49. The shaft 49 is supported at one end by a bearing 61 pressed on the end of the shaft and rotatable in a counterbore 63 of the bearing 51. Another portion of the shaft 49 is supported for rotation by an integral annular flange 65 of the tubular section 57. The bearing 61 may be constructed of stainless steel.

The rotor 47 includes a permanent magnet 67, a cap 69 of nonmagnetic material such as brass and a tube or cover 71 of nonmagnetic material such as aluminum. The cap 69 and the tube 71 are suitably interconnected as by an epoxy adhesive to form a well or receptacle. for the permanent magnet 67 which in turn is suitably connected to the cap and the tube as by an adhesive. The tube 71 completely encases the circumferential periphery of the permanent magnet 67 and the'cap 67 covers the righthand face (as viewed in FIG. 3) of the magnet 67. The torque arm 15 which is preferably constructed of a nonmagnetic material such as stainless steel has a plate portion 72 which is mounted on the lefthand face (as viewed in FIG. 3) of the permanent magnet 67 by an epoxy adhesive and/or spot welding.

One end of the shaft 49 is pressed into aperture of the cap 69 to thereby connect the shaft 49 and the cap 69 for rotation together. A torsion coil spring 73 has one end connected to the fixed bearing 51 and the other end connected to the rotatable cap 69 to thereby urge the rotor 47 and the torque arm 15 to the initial is established by the limits of travel of the driven member 19 or by engagement of the torque arm against a stop 75 which forms one end of the slot 31 in the stator section 21. A counterweight 76 is mounted on the cap 69 for rotation therewith to counterbalance the mass of the driven element 19.

The magnet 67 has an axial cylindrical aperture 77 extending therethrough. The magnet 67 is cylindrical except for diammetrically opposed, flat, parallel surfaces 79 and 81 which are perpendicular to a radially extending line and equidistant from the axis of rotation of the rotor 47. The magnet 67 is magnetized along a diametrically extending axis 83 which is parallel to the surfaces 79 and 81 with typical north/south polarity being indicated. The magnet 67 is symmetrical about the axis of magnetization 83.

In the initial or de-energized position, the torque arm 15 is ,in the position shown in FIG. 4 and is retained there by the return spring 73. In this position, the axis of magnetization 83 forms an angle a with a line drawn through the axis of rotation of the rotor and a central region of the slugs 25 and 27. In the embodiment illustrated, the angle a is approximately 12 (however, this angle can be varied depending upon the portion of the torque curve which is selected and the length of stroke required of the torque arm 15).

With-the coils 43 and 45 energized, the stator sections 21 and 23 form an electromagnet. For purposes of illustration, the stator sections 21 and 23 form south and north poles, respectively, to thereby cause each of the stator sections 21 and 23 to attract one pole of the permanent magnet 67 while repelling the other pole of the permanent magnet. Stated differently, the north pole of the permanent magnet 67 is repelled by the stator section 23 and attracted by the stator section 21 while the south pole of the permanent magnet is attracted by the stator section 23 and repelled by the stator section 21. This push-pull effect on the permanent magnet 67 produces substantial torque with the result that the rotor 47 and the torque arm, 15 rotate to a second orfinal position shown in FIG. 5. The second position is defined by the limits of travel of the driven member 19 or by a stop 85 which defines the other end of the slot 31' in the stator section 21.

As will be appreciated from FIG. 3, the magnet 67, the cap 69, the tube 71, the shaft 49 and the bearing 61 rotate while the bearing 51 is held stationary by virtue of its attachment to the stator sections 21 and 23. Moreover, such movement is accomplished against the biasing force of the torsion return spring 73. In the embodiment illustrated, the torque arm 15 and the rotor 47 rotate through an angle of 40, and this is a stroke of substantial length for rotary actuators of this general type.

The lines of flux extend through the cores 37 and 39 and through the stator sections 21 and 23. Because of the high reluctance of the slugs 25 and 27, the lines of flux extend across the small gap 87 between the rotor The spring 73 tends to return the torque arm 15 to the initail position shown in FIG. 4. In addition, when the coils 43 and 45 are de-energized, the rotor 47 inherently tends to return to the position in which the angle a (FIG. 4) is 0. This is caused by the natural tendency of the permanent magnet to center itself between the stator sections 21 and 23. The spring 73 is sufficiently strong to move the rotor through the position in which angle a equals 0 to a position such as that shown in FIG. 4 where angle a is greater than 0. The

purpose of this pull back of the rotor 47 is to select the most advantageous starting point on the torque versus displacement curve for this particular application.

FIGS. 4b and 40 show a modification of the present invention which is identical to the embodiment shown in FIGS. 1-5 except to the extent indicated herein. Corresponding parts are designated by corresponding reference characters followed by the letter a. In FIGS. 4b and 4c a rotary actuator 1 1a has stator sections 21a and 23a separated by regions of relatively high reluctance material which, in the embodiment illustrated, are brass slugs 25a and 27a. Unlike the construction shown in FIG. 4a, the brass slugs 25a and 27a extend axially and circumferentially of the rotor receiving aperture 29a. In all other respects, the rotary actuator 11a is identical to the rotary actuator 1 1. In the initial position the axis of magnetization 83a points at one end of the slug 27a; however, other orientations can be used. The slugs 25a and 27a extend circumferentially for the full arc of travel so that in the final position, the axis 830 points at the other end of the slug 27a.

The purpose of varying the shape of the high reluctance region between the stator sections 21a and 23a is to vary the shape of the torque curve obtainable. By causing the slug 25a to extend circumferentially in the direction of rotation, the so-called gap is effectively spread throughout at least a portion of the arc of travel of the rotor 47 This flattens the torque curve. I

FIGS. 6-8 show a rotary actuator 1 1b which is identical to the rotary actuator 11 except to the extent specifically noted herein. In FIGS. 6-8, portions corresponding to portions in FIGS. 1-5 are designated by corresponding reference characters followed by the letter 12. The actuator 11b is identical to the actuator 1 1 except that the latter has a rotor 47b which includes a pair of shoes 89 and 91, and the axis of magnetization 83b extends in a different direction relative to the permanent magnet 67b. The shoes 89 and 91 are identical and are constructed of highly permeable magnetic material such as soft iron. The shoes are suitably attached to the tube 71b and form arcuate peripheral segments of the rotor 47. The advantage of the shoes 89 and 91 is to provide a low reluctance path for the lines of flux between the stator sections 21b and 23b to thereby improve the torque.

The torque curve can also be shaped by appropriately shaping the'shoes as shown, for example, in FIG. 7. The shoe 91 has a ramp or tapered'portion 93 and a maximum axial length portion 95 with the tip 97 of the ramp being adjacent the slug 27b in the initail position shown in FIG. 6. The shoe 89 is identical in construction to the shoe 91 and has a ramp 98 with a tip 99 which confronts the slug 25b in the initial position. As the rotor rotates from the initial position shown in FIG. 6 toward the second position shown in FIG. 8, there is a continuous increase in perrneance due to the increase in the amount of the highly permeable shoes 89 and 91 which confront the slugs 25b and 27b, respectively. As torque is proportional to the change in perrneance, the result is an increase in torque and a flattening of the torque curve. In the'embodirnent illustrated, the ramp 93 extends circumferentially for the arc of travel of the rotor 47b, and accordingly, there is a continuing increase in perrneance throughout the full stroke of the rotor 47 b.

Another feature of the present invention is the angle of the axis 83b with respect to the central transverse axis 101 of the rotor 47b. The axes 83b and 101 form an angle b which in the embodiment illustrated is 55 and which in the embodiment of FIGS. 1-5 was The axis 83b extends through the axis of rotation of the rotor 47b in a direction transverse thereto and substantially intersects the zone of intersection between the flat'and arcuate peripheral surface portions 79b and 105, respectively, of the rotor 47. In the de-energized condition, the rotor 47b tends to orient itself so that the axis 83b points generally toward the slug 25b.

The advantage of this construction is two-fold. First, in the initial position there is a relatively large gap between the planar surface 79b and the confronting arcuate surface portion of the rotor receiving aperture 29b. Accordingly, the performance of the gap is relatively high due to this relatively wide spacing. However, as the rotor rotates toward the final position shown in FIG. 8, the cylindrical surface portion 105 is progressively brought into registry with the surfaces of the rotor receiving aperture 29b on both sides of the slugs 27b with the result that perrneance is increased. This change in perrneance increases torque.

Secondly, the inherent tendency of the rotor to return to the position of FIG. 6 is reduced so that if pull back of the rotor 47b is desired to from an angle a such as in FIG. 4, it can be accomplished with a relatively weak return spring.

FIGS. 9 and 10 illustrates a rotary actuator 110 which is identical to the rotary actuator 11 in all respects not specifically noted herein. The actuator 110 has a torque arm 150 which is rotatable in either direction from the centered position shown in FIG. 9. In the centered or initial position shown in FIG. 9, the axis of magnetization 830 of the magnet 670 points toward the slug 27c. By energizing the windings 43c and 45:: in one direction, the force field generated rotates the rotor 470 in the clockwise direction and by energizing the coils in the reverse direction, the rotor rotates in the counter clockwise direction. The forces operating on the rotor 470 to rotate the latter are substantially identical to those described hereinabove.

A return or centering spring 1 l 1 is utilized to bias the rotor 47c toward the neutral position. In the embodiment illustrated, the spring 11 includes a loop section 113 suitably affixed to the tubular section 57c and a pair of resilient legs 1 l5 and 117. A pin 1 19 is mounted on the rotor 47c for movement therewith and projects between the two legs 115 and 117. A fixed pin 121 is s uitablymounted such as on the plate 530 and projects between the legs 115 and 117. With this construction, clockwise rotation of the rotor (as viewed in FIG. 9) is resisted by the resilient leg 115 and counter clockwise rotation of the rotor is resisted by the resilient leg 117.

The return spring 73 provided in the embodiment of FIG. 1 is eliminated.

Although exemplary embodiments of the invention have been shown and described, many changes, modifications, and substitutions may be made by one having ordinary skill in the art without necessarily departing from the spirit and scope of this invention.

I claim:

1. A rotary actuator comprising:

first and second stator sections, each of said stator sections including magnetic material;

means for mounting said stator sections with said stator sections being separated by a relatively high reluctance region;

a rotor including a permanent magnet having first and second poles of opposite polarity;

means for mounting said rotor for rotation about an axis with the rotor being adjacent said stator sections, said rotor being rotatable from a first position through a predetermined number of degrees about said axis to a second position;

said stator sections extending for a substantial distance around the rotor in a direction circumferentially of the axis of rotation;

first electrical means for magnetizing said stator sections to move said rotor from said first position to said second position, at least one zone of said first stator section attracting said permanent magnet toward said second position and at least one zone of said second stator section repelling said permanent magnet from said first position toward said second position;

said rotor including a segment constructed of magnetic material which is not permanently magnetized and located adjacent the periphery of the rotor; and

said segment being a. first peripheral surface segment, said rotor having a second peripheral surface segment intersecting said first peripheral surface segment at a zone of intersection, said surface segments being of different configurations, said magnet having an axis of magnetization extending generally toward the zone of intersection.

2. A rotary actuator as defined in claim 18 including biasing means for urging said rotor from said second position toward said first position.

3. A rotary actuator as defined in claim 1 wherein said relatively high reluctance region is a first region, said stator sections being separated by a second relatively high reluctance region, said first and second stator sections extending substantially completely around said rotor, said first stator section attracting one pole of said permanent magnet and repelling the other pole of said permanent magnet when the first electrical means is energized and said second stator section attracting said other pole of said permanent magnet and repelling said one pole of said permanent magnet when said first electrical means is energized.

4. A rotary actuator as defined in claim 1 wherein said region extends circumferentially of said rotor as it extends between said stator sections to thereby affect the torque of said rotor as said rotor rotates from said first position to said second position.

5. A rotary actuator comprising:

first and second stator sections, each of said stator sections including magnetic material;

means for mounting said stator sections with said stator sections being separated by a relatively high reluctance region;

a rotor including a permanent magnet having first and second poles of opposite polarity;

means for mounting said rotor for rotation about an axis with the periphery of said rotor being closely adjacent said stator sections;

the dimension of said region circumferentially of said axis being relatively small when compared with the circumferential dimension of said stator sections circumferentially of said axis;

said rotor including a segment adjacent the periphery thereof of substantially nonmagnetized, magnetizable material; and

electrical means for magnetizing said stator sections to rotate the rotor from a first position to a second position, at least one zone of said first stator sec- I tion attracting said permanent magnet from said first position toward said second position and at least one zone of said second stator section repelling said permanent magnet from said first position toward said section position, said electrical means setting up a force field having lines of flux which pass from one of said stator sections through said segment of said rotor to the other of said stator sections.

6. A rotary actuator as defined in claim 5 wherein the axial dimension of at least a portion of said segment tapers circumferentially of the rotor.

7. A rotary actuator as defined in claim 5 wherein said magnet has an axis of magnetization and a central transverse axis, said axes being nonparallel.

l I i 

1. A rotary actuator comprising: first and second stator sections, each of said stator sections including magnetic material; means for mounting said stator sections with said stator sections being separated by a relatively high reluctance region; a rotor including a permanent magnet having first and second poles of opposite polarity; means for mounting said rotor for rotation about an axis with the rotor being adjacent said stator sections, said rotor being rotatable from a first position through a predetermined number of degrees about said axis to a second position; said stator sections extending for a substantial distance around the rotor in a direction circumferentially of the axis of rotation; first electrical means for magnetizing said stator sections to move said rotor from said first position to said second position, at least one zone of said first stator section attracting said permanent magnet toward said second position and at least one zone of said second stator section repelling said permanent magnet from said first position toward said second position; said rotor including a segment constructed of magnetic material which is not permanently magnetized and located adjacent the periphery of the rotor; and said segment being a first peripheral surface segment, said rotor having a second peripheral surface segment intersecting said first peripheral surface segment at a zone of intersection, said surface segments being of different configurations, said magnet having an axis of magnetization extending generally toward the zone of intersection.
 2. A rotary actuator as defined in claim 18 including biasing means for urging said rotor from said second position toward said first position.
 3. A rotary actuator as defined in claim 1 wherein said relatively high reluctance region is a first region, said stator sections being separated by a second relatively high reluctance region, said first and second stator sections extending substantially completely around said rotor, said first stator section attracting one pole of said permanent magnet and repelling the other pole of said permanent magnet when the first electrical means is energized and said second stator section attracting said other pole of said permanent magnet and repelling said one pole of said permanent magnet when said first electrical means is energized.
 4. A rotary actuator as defined in claim 1 wherein said region extends circumFerentially of said rotor as it extends between said stator sections to thereby affect the torque of said rotor as said rotor rotates from said first position to said second position.
 5. A rotary actuator comprising: first and second stator sections, each of said stator sections including magnetic material; means for mounting said stator sections with said stator sections being separated by a relatively high reluctance region; a rotor including a permanent magnet having first and second poles of opposite polarity; means for mounting said rotor for rotation about an axis with the periphery of said rotor being closely adjacent said stator sections; the dimension of said region circumferentially of said axis being relatively small when compared with the circumferential dimension of said stator sections circumferentially of said axis; said rotor including a segment adjacent the periphery thereof of substantially nonmagnetized, magnetizable material; and electrical means for magnetizing said stator sections to rotate the rotor from a first position to a second position, at least one zone of said first stator section attracting said permanent magnet from said first position toward said second position and at least one zone of said second stator section repelling said permanent magnet from said first position toward said section position, said electrical means setting up a force field having lines of flux which pass from one of said stator sections through said segment of said rotor to the other of said stator sections.
 6. A rotary actuator as defined in claim 5 wherein the axial dimension of at least a portion of said segment tapers circumferentially of the rotor.
 7. A rotary actuator as defined in claim 5 wherein said magnet has an axis of magnetization and a central transverse axis, said axes being nonparallel. 